The present invention relates to electrical power devices and methods of operation thereof, and more particularly, to power conversion devices and methods of operation thereof.
Uninterruptible power supplies (UPSs) are power conversion devices that are commonly used to provide conditioned, reliable power for computer networks, telecommunications networks, medical equipment and the like. UPSs are widely used with computers and similar computing devices, including but not limited to personal computers, workstations, mini computers, network servers, disk arrays and mainframe computers, to insure that valuable data is not lost and that the device can continue to operate notwithstanding temporary loss of an AC utility source. UPSs typically provide power to such electronic equipment from a secondary source, such as a battery, in the event that a primary alternating current (AC) utility source drops out (blackout) or fails to provide a proper voltage (brownout).
Conventional UPSs may be classified into categories. Referring to FIG. 1, a typical conventional off-line UPS disconnects a load from a primary AC source 10 when the primary AC source fails or is operating in a degraded manner, allowing the load to be served from a secondary source such as a battery. The AC power source 10 is connected in series with a switch SI, producing an AC voltage across a load 20 when the switch S1 is closed. Energy storage is typically provided in the form of a storage capacitor CS. The secondary power source, here a battery B, is connected to the load 20 via a low voltage converter 30 and a transformer T. When the AC power source 10 fails, the switch SI is opened, causing the load to draw power from the battery B. The low voltage converter 30 typically is an inverter that produces a quasi-square wave or sine wave voltage on a first winding L1 of the transformer T from a DC voltage produced by the battery B. The first winding L1 is coupled to a second winding L2 of the transformer T connected across the load 20. When the AC power source is operational, i.e., when the switch S1 is closed, the battery B may be charged using the low-voltage converter 30 or a separate battery charger circuit (not shown).
A line interactive (LIA) UPS topology is illustrated in FIG. 2. Here, the transformer T has a third winding L3 that may be connected in series with the load 20 using switches S2, S3 to xe2x80x9cbuckxe2x80x9d or xe2x80x9cboostxe2x80x9d the voltage applied to the load 20. As with the offline UPS topology of FIG. 1, when the AC power source 10 fails, the switch S1 can be opened to allow the load 20 to run off the battery B.
As illustrated in FIG. 3, a typical on-line UPS includes a rectifier 40 that receives an AC voltage from an AC power source 10, producing a DC voltage across a storage capacitor CS at an intermediate node 45. An inverter 50 is connected between the intermediate node 45, and is operative to produce an AC voltage across a load 20 from the DC voltage. As shown, a battery B is connected to the intermediate node 45 via a DC/DC converter 60, supplying auxiliary power. Alternatively, the DC/DC converter can be eliminated and a high-voltage battery (not shown) connected directly to the intermediate node 45.
Each of these topologies may have disadvantages. For example, typical conventional on-line and LIA UPSs for 60 Hz applications use 60 Hz magnetic components (e.g., transformers and inductors) that are sized for such frequencies, and thus may be large, heavy and expensive. LIA UPSs often exhibit step voltage changes that can affect the performance of the load. Conventional off-line, LIA and on-line UPSs often use large storage capacitors, which tend to be bulky and expensive, in order to maintain an acceptable output voltage under heavy loading conditions. Moreover, because conventional UPSs are typically designed to operate in only one of the above-described off-line, LIA or on-line modes, sellers of UPSs may be required to maintain large inventories including several different types of UPSs in order to meet a variety of different customer applications.
According to embodiments of the present invention, a power converter, such as one that might be utilized in an uninterruptible power supply (UPS), includes first and second voltage busses, a first input port having a first terminal coupled to one of the first and second voltage busses, a neutral bus and an output terminal. A first switching circuit selectively couples a second terminal of the first input port to the first and second voltage busses. A second switching circuit selectively couples the first and second voltage busses to the output terminal. A third switching circuit selectively couples the first and second voltage busses to the neutral bus. Preferably, the first, second and third switching circuits are operative to produce an AC output voltage at the output terminal from a DC input voltage at the first input port such that alternating ones of the first and second terminals of the first input port are referenced to the neutral bus for successive first and second half cycles of the AC output voltage.
In embodiments of the present invention, the first switching circuit includes a first inductance having first and second terminals, the first terminal of the first inductance coupled to the second terminal of the first input port. The first switching circuit further includes a first switch is operative to couple and decouple the second terminal of the first inductance and the first voltage bus and a second switch operative to couple and decouple the second terminal of the first inductance and the second voltage bus. The second switching circuit includes a second inductance having first and second terminals, the first terminal of the second inductance coupled to the output terminal. The second switching circuit further includes a third switch operative to couple and decouple the second terminal of the second inductance and the first voltage bus and a fourth switch operative to couple and decouple the second terminal of the second inductance and the second voltage bus. The third switching circuit includes a third inductance having first and second terminals, the first terminal of the third inductance connected to the neutral bus. The third switching circuit also includes a fifth switch operative to couple and decouple the second terminal of the third inductance and the first voltage bus and sixth switch operative to couple and decouple the second terminal of the third inductance and the second voltage bus.
In other embodiments of the present invention, a power converter further includes a second input port. A fourth switching circuit concurrently couples the second terminal of the first input port to the second voltage bus, decouples the second terminal of the first input port from the first switching circuit, and couples the first switching circuit to a first terminal of the second input port, in a first mode. The fourth switching circuit concurrently couples the second terminal of the first input port to the first switching circuit, decouples the second terminal of the first input port from the second voltage bus, and decouples the first terminal of the second input port from the first switching circuit, in a second mode.
According to other aspects of the present invention, a power converter includes first and second voltage busses, a neutral bus, and an output terminal. A DC voltage generating circuit is operative to produce respective first and second DC voltages on the first and second voltage busses. A first switching circuit is operative to selectively couple the first and second voltage busses to the output terminal. A storage circuit is connected to the output terminal, and includes a capacitive storage element, a rectifying circuit coupling the capacitive storage element to the output terminal and operative to produce a DC voltage across the capacitive storage element from an AC output voltage at the output terminal, and a second switching circuit operative to selectively couple the capacitive storage element to the output terminal.
In embodiments of the present invention, the first switching circuit includes a first inductor having first and second terminals. The first terminal of the first inductor is coupled to the output terminal and respective first and second switches are operative to selectively couple the second terminal of the inductor to the first and second voltage busses. The storage circuit is electrically coupled to the output terminal through a second inductor that is inductively coupled to the first inductor.
According to still other embodiments of the present invention, the storage circuit includes first and second storage busses. The capacitive storage element includes respective first and second capacitors coupling respective ones of the first and second storage busses to the neutral bus. The second switching circuit includes a third switch operative to couple and decouple the first storage bus and the output terminal and a fourth switch operative to couple and decouple the second storage bus and the output terminal. According to an aspect of the present invention, the first and third switches open and close in synchronism, and the second and fourth switches open and close in synchronism.
According to other aspects of the present invention, the DC voltage generating circuit includes a rectifying circuit configured to connect to an AC power source at an AC input port and operative to produce the first and second DC voltages on the first and second voltage busses from an AC input voltage applied to the DC voltage generating circuit. The rectifying circuit, the first switching circuit and the second switching circuit are operative to produce the AC output voltage at the output terminal while maintaining a substantially unity power factor at the AC input port.
According to method aspects of the present invention, an AC output voltage is generated at a load from a DC input voltage produced by a DC power source by coupling a first terminal of the DC power source to one of a first voltage bus and a second voltage bus. A second terminal of the DC power source is selectively coupled to the first voltage bus and a second voltage bus through respective first and second switches. A first terminal of a load is coupled to a neutral bus. The first and second voltage busses are selectively coupled to a second terminal of the load through respective third and fourth switches. The first and second voltage busses are selectively coupled to the neutral bus through respective fifth and sixth switches. Preferably, the first and second terminals of the DC power source are alternatingly referenced to the neutral bus for successive first and second half cycles of the AC output voltage.
According to other method aspects of the present invention, an AC output voltage is produced at a load by generating respective first and second DC voltages on the first and second voltage busses. The first and second voltage busses are selectively coupled to the load through respective first and second switches to generate an AC output voltage at the load. First and second capacitors are rectifyingly coupled to the load to produce respective first and second DC voltages across respective ones of the first and second capacitors from an AC output voltage at the load. The first and second capacitors are selectively coupled to the load through respective third and fourth switches to transfer power between the first and second capacitors and the load.